The present invention generally relates to a device for protecting threaded couplings manufactured in accordance with the specifications of the American Petroleum Institute (hereinafter referred to as A.P.I.). In particular, the present invention is related to a device for protecting not only the threaded cavities of such A.P.I. couplings but also a seal ring seated therein. Thus, the device according to the present invention provides protection to threaded seal-ring forms of A.P.I. couplings from environmental damage and, additionally, provides a measure of protection from mechanical damage for all tubing and casing couplings manufactured in accordance with A.P.I. specifications.
In practice, couplings having A.P.I. threads are utilized to join tubing or casing joints (e.g., lengths of conduit or pipe) together for the purpose of completing oil and/or natural gas production wells, injection wells, storage wells, flow lines, and other instances where piping connections are necessary. Most, if not all, couplings presently manufactured by domestic and foreign steel mills or other manufacturers are of the type having only an inwardly tapered threaded cavity. Such couplings having only an inwardly tapered threaded cavity in accordance with A.P.I. specifications will be hereinafter referred to as "standard A.P.I. couplings" (see FIG. 1).
In situations where high pressures and extreme temperatures are encountered during the well-drilling process, a connection is needed which provides a constant leak-proof barrier when the tubing joints or successive lengths of casing joints are coupled together. Accordingly, in order to overcome the problems of high pressure wells in such situations, an A.P.I. coupling having machined retaining grooves with Teflon-type seal rings inserted therein was developed, as exemplified by U.S. Pat. No. 2,980,451 to Taylor et al, the entire disclosure of which is incorporated herein by reference. Such couplings having trapped seal rings shall be hereinafter referred to as "grooved couplings" (see FIG. 2). Grooved couplings increase the leak resistance of standard A.P.I. threaded couplings by providing an occlusive barrier against the seepage of gases and liquids when successive lengths of pipes or casing joints are coupled together, especially where high pressures are encountered.
As mentioned above, in practice the standard A.P.I. coupling is practically the only type that is manufactured at steel mills and other manufacturing facilities. The decision to modify the standard A.P.I. coupling into a grooved coupling is entirely left up to the discretion of the end user (e.g., petroleum companies, well drilling companies, or the like). If, in the discretion of such companies, it is decided that grooved couplings are necessary for the particular environment in which they are to be utilized, there are in existence several companies which can produce a grooved coupling by having the seal rings inserted into grooves machined into the standard A.P.I. coupling.
In order to transport the grooved couplings from the modifications facility to the location where they will usually be placed into service, protectors to protect the threaded cavity and the seal rings are usually desirable. However, traditionally the type of protector which is utilized for the grooved couplings is the same as the protector utilized for standard A.P.I. couplings to protect the threaded cavity thereof during transportation and handling.
When utilized in conjunction with grooved couplings, the conventional protectors that are manufactured for the standard A.P.I. couplings have been found to be insufficient for their intended purpose. Since the grooved coupling includes seal rings seated therein, the protector for the standard A.P.I. coupling cannot be threadably engaged beyond the location of the seal ring. Thus, the protector only engages a portion of the threads above the seal ring in the grooved couplings. The conventional protector, therefore, is extremely susceptible to loose fitting engagement and, in most cases, will be disengaged from the coupling during transportation thereby obviating its intended protective function. Thus, the need in the art for protectors capable of complete protection for grooved couplings has been apparent, yet until the present invention, this need had remained unanswered.
Of course, others in this art have developed various means for protecting pipe threads or the like as exemplified by U.S. Pat. Nos. 1,640,696; 1,675,143; 2,893,437; 3,285,289 and 4,119,121. For example, U.S. Pat. No. 2,893,437 discloses a protector nipple having upper and lower threaded portions and a relatively smooth shoulder portion so as to facilitate quick, threaded connection of the nipple within the end of a threaded pipe or coupling. Another type of "quick" threaded connecting structure can be seen in U.S. Pat. No. 2,587,544. U.S. Pat. Nos. 1,675,143 and 1,640,969 relate specifically to various contrivances for protecting the threads of pipe and/or well drilling tools from damage, while U.S. Pat. No. 4,119,121 relates to a plastic closure securely insertable into the end of a pipe to protect the threads thereof from damage. Further, U.S. Pat. No. 3,285,289 proposes an adjustable clean-out for a sanitary plumbing system and includes a relatively smooth, cylindrical outer surface for slidably engaging with an O-ring therein.
However, such prior art pipe thread protectors or the like are not suitable for use with grooved A.P.I. couplings as is apparent when detailed consideration is given to the disclosures of the above-cited patents.
The present invention, however, provides a coupling adapted for threaded cooperation with grooved A.P.I. couplings and eliminates the problems associated with conventional protectors. Accordingly, a primary object of the present invention is to provide a device which is capable of threaded engagement with grooved A.P.I. couplings so as to protect not only the inwardly tapered threaded cavity of such couplings, but also the seal ring thereof from potential mechanical and environmental damage during transportation and handling until it is desired to be placed into service.
Other objects and advantages of the present invention will become more clear to those skilled in the art after careful consideration is given to the detailed description of the preferred exemplary embodiments which follow.